Vinyl fluoride (PVF) and vinylidene fluoride (PVdF) are thermoplastic polymers which exhibit a combination of advantageous properties and in particular, a high chemical inertness and an excellent resistance to ultraviolet rays.
Polycarbonate (PC) films generally have acceptable levels of clarity, and strength, but lack acceptable levels of birefringence, chemical and UV radiation resistance for exterior automotive applications. For example, PC films generally have high birefringence, which is, in part, due to the levels of stress which are placed on the film during its formation. This stress is frozen into the film upon cooling.
It is generally known in theory to produce PC films by extruding heated resin and passing the extruded resin through the nip formed between two polished metal rolls. This process is typically unsuitable for producing low birefringence films because it introduces a high level of stress in the films which increases the birefringence of said films. A low birefringence film is required for 3-dimensional thermoformed (vacuum or pressure forming) articles prepared by IMD for applications that require tight graphics registration. Low birefringence provides part to part dimensional consistency and printing registration wherein the decorated film is formed using heat.
In U.S. Pat. Nos. 4,659,625 and 5,096,782 issued to Solvay & Cie, a laminated structure, which comprises a layer of PVdF bonded to a layer of PC using a vinyl acetate polymer, is assembled by heat lamination or coextrusion. This prior art suffers from the lack of low birefringence in the laminated structure.
In U.S. Pat. No. 5,304,413 issued to DuPont, a laminated structure which comprises a layer of PVF bonded to a layer of PC using an acrylic polymer, is assembled by heat lamination. This prior art also suffers from lack of low birefringence in the laminated structure.